Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/136

Then—

}}

and the moment of that pressure relative to a horizontal axis at the level of the ground is

Let h be the height above the ground at which the strut abuts against the dam, and i its inclination to the horizon ; the thrust along the strut is

T = Msec. i-S-h,

from which the scantling required, depending on the sort of timber employed, can be calculated.

ELEVATION

PLAN

Fig. 3.—Cofferdam for Hard Bottom.

A. High Water; B. Low Water.

In conclusion it may be noticed that the introduction of iron cylinders and compressed air for founding the piers of bridges has not on]y superseded the use of timber coffer-dams for piers in soft bottoms, but has enabled bridges to be securely placed in situations where no timber dams could have answered the purpose. On the other hand, there are many engineering works connected with river, harbour, and dock improvements, to which the cylinder system is quite inapplicable, and for which extensive and costly coffer-dam^ of the kind we have described must continue to be employed. The method of founding by iron cylinders has been described in the article Bridge, to which the reader

is referred.

(d. s.)

COGNAC, a town of France, at the head of an arron- dissement in the department of Charente, on the left bank of the River Charente, about 32 miles by rail west of Angouleme. It has a tribunal of commerce, a communal college, a prison, a hospital, a church of the 12th cen tury dedicated to St Leger, and an old castle, now used as a wine-store, in the park of which is a bronze statue of Francis L, marking the spot where, according to tradition, he was born in 1494. The most important industry of Cognac is the distillation and exportation of the celebrated brandy to which the town gives its name (see Brandy). Iron is also manufactured, and a considerable trade is main tained in grain and cattle. Cognac is probably to be identified with one of the many places that bore the name of Condate ; it was known as Coniacum in the Middle Ages. At an early period it was governed by lords of its own, but in the 12th century it became subject to the counts of Angoumois. In 1238 it was the seat of an ecclesiastical council summoned by Gerard of Bordeaux ; arid in 1526 it gave its name to a treaty concluded against Charles V. by Francis I., Henry VIII. of England, the Pope, Venice, and Milan. In 1562 the town was captured by the Huguenots, and in 1651 it defied the prince of Conde. Before the Revolution it possessed a fine Benedictine monastery and two other convents. The population, which was only 4000 about the middle of the 18th century, had increased by 1872 to 12,950.

COHESION. See Attraction, Capillary Action, and Constitution of Bodies.

COHOES, one of the most important manufacturing centres in the United States, is situated in Albany County, in the State of New York, at the confluence of the Mohawk with the Hudson, just below the famous Cohoes fall on the former river, to which it is indebted for its prosperity. It contains seven churches and twenty-two public schools, the most remarkable of the churches being the Roman Catholic St Bernard s and the Episcopal St John s. The manufacturing establishments comprise six cotton mills with 4000 looms, eighteen knitting mills, a rolling mill, a pin factory, a knitting-needle factory, two foundries, three machine shops, a paper-mill, and a bedstead factory. In 1870 there were produced 54,342,000 yards of cloth, 33,600,000 knitting-needles, and 350,000 pack ages of pins ; while the turn-out of hosiery formed a third of the whole amount manufactured in the United States. The whole water-power of the river for somo distance both above and below the falls is the property of the Cohoes Company instituted in 1826; and the various manu factories obtain their share at a fixed annual charge for each horse-power. The supply is regulated by a dam erected above the falls in 1865, and by a system of five canals. Cohoes owes its rise to the incorporation of the Cohoes Manufactuiing Company in 1811. It obtained the rank of a village in 1848 and that of a city in 1869. Its population in 1850 was 4229 ; in 1860, 8800 ; and in 1870, 15,357. A large number of French Canadians are to be found among the operatives.

COIMBATORE, a district of British India, in the Presidency of Fort St George or Madras, situated between

10* 45 and 11 48 N. lat. and between 76 50 and 78 10 E. long. It is bounded on the N. by Mysore, on the E. by the district of Salem, the Cauveri River marking the entire boundary line, on the S. by Madura and Travancore State,

and on the W. by Cochin State, Malabar District, and the